The present invention relates generally to batteries, and more particularly relates to air managers for metal-air cells.
Metal-air cells have been recognized as a desirable means for powering portable electronic equipment such as personal computers and camcorders because such cells have a relatively high power output with relatively low weight as compared to other types of electrochemical cells. Metal-air cells utilize oxygen from the ambient air as a reactant in the electrochemical process rather than a heavier material, such as a metal or metallic composition.
Metal-air cells use one or more oxygen electrodes separated from a metallic anode by an aqueous electrolyte. During the operation of a metal-air cell, such as a zinc-air cell, oxygen from the ambient air and water from the electrolyte are converted at the oxygen electrode to hydroxide ions and zinc is oxidized at the anode and reacts with the hydroxide ions, such that water and electrons are released to provide electric energy.
Metal-air cells are often arranged in multiple cell battery packs within a common housing to provide a sufficient amount of electrical power. The result is a relatively light-weight battery. A supply of air must be supplied to the oxygen electrodes of the battery pack in order for the battery pack to supply electricity. Some prior systems sweep a continuous flow of fresh air from the ambient environment across the oxygen electrodes at a flow rate sufficient to achieve the desired power output. Such an arrangement is shown in U.S. Pat. No. 4,913,983 to Cheiky. Cheiky uses a fan within air from the ambient environment to the oxygen the battery housing to supply the flow of 1 electrodes. When the Cheiky battery is turned on an air inlet and an air outlet, which are closed by one or more xe2x80x9cair doorsxe2x80x9d while the battery is turned off, are opened and the fan is operated to create the flow of air into, through, and out of the housing. Thus, the air doors are closed when the battery is turned off to isolate the cells from the environment. Although the mechanical air doors may limit the transfer of oxygen, water vapor, and contaminates into and out of the housing, such mechanical air doors add complexity to the battery housing itself and, inevitably, increase the size and cost of the overall battery pack.
In contrast to the nonrecirculating arrangement of Cheiky, U.S. Pat. No. 5,691,074 to Pedicini discloses a system in which a fan recirculates air across the oxygen electrodes of metal-air battery. The fan also forces air through one or more openings to refresh the recirculating air. The cells provide an output current while the fan is operating but experience minimal discharge while the fan is not operating and the opening or openings remain unsealed. That is, the Pedicini metal-air battery has a long shelf life without requiring operation of air doors, or the like, to open and close the opening or openings. The opening or openings are sized to restrict air flow therethrough while the opening or openings are unsealed and the fan is off.
The restrictive air openings of Pedicini, as well as the air doors of Cheiky, function to substantially isolate the metal-air cells from the ambient environment while the battery is not operating. Isolating the metal-air cells from the ambient environment while the battery is not operating increases the shelf life of the battery and also decreases the detrimental impact of the ambient humidity level on the metal-air cells. Exposed metal-air cells may absorb water from the air through the oxygen electrode and fail due to a condition called flooding, or they may release water vapor from the electrolyte through the oxygen electrode and fall due to drying.
Typically metal-air cells are designed to have a relatively large oxygen electrode surface, so that the largest power output possible can be obtained from a cell of a given volume and weight. Once air is introduced into a metal-air battery housing, the oxygen-bearing air is distributed to all oxygen electrode surfaces. However, in multiple cell systems it is common for an air distribution path to extend from a fan for a lengthy distance and sequentially across oxygen electrode surfaces. Oxygen may be depleted from the air stream flowing along the distribution path so that the oxygen concentration at the end of the distribution path falls below a level desired for optimal power production from all the cells. As a result of the nonuniform air flow distribution, each of the cells may operate at a different current (when the cells are arranged in parallel) and voltage (when the cells are arranged in series), which is not optimal.
If one uses such an air distribution path or paths with a flow through system as in Cheiky, the oxygen depletion problem may be overcome by moving a large volume of air through the battery housing so that the amount of oxygen removed from the air flow in the upstream portions of the distribution path has a negligible impact on the oxygen concentration in downstream portions of the distribution path. However, using such a large volume of fresh air may subject the battery to the flooding or drying problems described above. Pedicini at least partially resolves the flooding or drying out problems by recirculating air within the battery housing and continuously replenishing a portion of the recirculated air. Pedicini may nonetheless experience some oxygen depletion problems if using an air distribution path that extends from a fan for a lengthy distance and sequentially across oxygen electrode surfaces.
One drawback with the current design of metal-air cells is that the cells tend to be somewhat larger in size than conventional electrochemical power sources. This size constraint is caused, in part, by the requirements of having an anode, a cathode, an electrolyte, a cell casing of some sort, and an air manager or an air passageway of some sort to provide the reactant air to the cell. These elements all take up a certain amount of valuable space.
In attempting to design smaller metal-air cells and batteries, one concern is to provide a sufficient amount of air to operate the cells at their desired capability while also preventing too much air from reaching the cells during periods of non-use. A vast improvement in air manager technology is found in the above-mentioned U.S. Pat. No. 5,691,074, entitled xe2x80x9cDiffusion Controlled Air Vent for a Metal-Air Batteryxe2x80x9d to Pedicini, which is incorporated herein by reference. Pedicini discloses, in one embodiment, a group of metal-air cells isolated from the ambient air except for an inlet and an outlet passageway. These passageways may be, for example, elongate tubes. An air-moving device positioned within the housing forces air through the inlet and outlet passageways to circulate the air across the oxygen electrodes and to refresh the circulating air with ambient air. The passageways are sized to allow sufficient airflow therethrough while the air mover is operating but also to restrict the passage of water vapor therethrough while the passageways are unsealed and the air mover is not operating.
When the air mover is off and the humidity level within the cell is relatively constant, only a very limited amount of air diffuses through the passageways. The water vapor within the cell protects the oxygen electrodes from exposure to oxygen. The oxygen electrodes are sufficiently isolated from the ambient air by the water vapor such that the cells have a long xe2x80x9cshelf lifexe2x80x9d without sealing the passageways with a mechanical air door. These passageways may be referred to as xe2x80x9cdiffusion tubesxe2x80x9d, xe2x80x9cisolating passagewaysxe2x80x9d, or xe2x80x9cdiffusion limiting passagewaysxe2x80x9d due to their isolating capabilities.
The isolating passageways act to minimize the detrimental impact of humidity on the metal-air cells, especially while the air-moving device is off. A metal-air cell that is exposed to ambient air having a high humidity level may absorb too much water through its oxygen electrode and fail due to a condition referred to as xe2x80x9cflooding.xe2x80x9d Alternatively, a metal-air cell that is exposed to ambient air having a low humidity level may release too much water vapor from its electrolyte through the oxygen electrode and fail due to a condition referred to as xe2x80x9cdrying out.xe2x80x9d The isolating passageways limit the transfer of moisture into or out of the metal-air cells while the air moving device is off, so that the negative impacts of the ambient humidity level are minimized.
The efficiency of the isolating passageways in terms of the transfer of air and water into and out of a metal-air cell can be described in terms of an xe2x80x9cisolation ratio.xe2x80x9d The xe2x80x9cisolation ratioxe2x80x9d is the rate of the water loss or gain by the cell while its oxygen electrodes are fully exposed to the ambient air as compared to the rate of water loss or gain by a cell while its oxygen electrodes are isolated from the ambient air except through one or more limited openings. For example, given identical metal-air cells having electrolyte solutions of approximately thirty-five percent (35%) KOH in water, an internal relative humidity of approximately fifty percent (50%), ambient air having a relative humidity of approximately ten percent (10%), and no fan-forced circulation, the water loss from a cell having an oxygen electrode fully exposed to the ambient air should be more than 100 times greater than the water loss from a cell having an oxygen electrode that is isolated from the ambient air except through one or more isolating passageways of the type described above. In this example, an isolation ratio of more than 100 to 1 should be obtained.
In accordance with the above-referenced example from Pedicini, the isolating passageways function to limit the amount of oxygen that can reach the oxygen electrodes when the fan is off and the internal humidity level is relatively constant. This isolation minimizes the self-discharge and leakage or drain current of the metal-air cells. Self-discharge can be characterized as a chemical reaction within a metal-air cell that does not provide a usable electric current. Self-discharge diminishes the capacity of the metal-air cell for providing a usable electric current. Self-discharge occurs, for example, when a metal-air cell dries out and the zinc anode of oxidized by the oxygen that seeps into the cell during periods of non-use. Leakage current, which is synonymous with drain current, can be characterized as the electric current that can be supplied to a closed circuit by a metal-air cell when air is not provided to the cell by an air moving device. The isolating passageways as described above may limit the drain current to an amount smaller than the output current by a factor of at least fifty (50) times.
In addition to humidity differentials, the isolation ratio appears to be dependent upon the pressure differential that can be induced by the fan or other type of air mover and the degree to which the isolating passageways slow the diffusion of air and water when the fan is off. In the past, air moving devices used in metal-air batteries have been bulky and expensive relative to the volume and cost of the metal-air cells. Although a key advantage of metal-air cells is their high energy density resulting from the low weight of the oxygen electrode, this advantage is compromised by the space and weight required by an effective air-moving device. Space that otherwise could be used for battery chemistry to prolong the life of the battery must be used to accommodate an air-moving device. Increasing the size and power of the fan or lengthening the isolating passageways to increase the isolation ratio, however, generally would lead one to increase the size of the cell or the battery. In other words, attempts to reduce the size of the cell or the battery have been somewhat limited by the need for an adequate isolation ratio and an adequately sized fan or air mover. This loss of space can be critical to attempts to provide a practical metal-air cell in small enclosures such as the xe2x80x9cAAxe2x80x9d cylindrical size now used as a standard in many electronic devices.
Even though numerous improvements to air managers for metal-air cells have been previously disclosed, there is always a desire for air managers that cooperate with metal-air cells in a manner that further enhances the efficiency, power and lifetime of the metal-air cells. For example, further advances in the area of evenly distributing oxygen laden air across the oxygen electrodes in a metal-air battery should further enhance the efficiency, power and lifetime of metal-air batteries.
There is a need, furthermore, for a metal-air cell and/or battery pack that is as small and compact as possible, that occupies less of the volume available for battery chemistry, and provides adequate power with an adequate isolation ratio. These advantages must be accomplished in a metal-air cell or battery pack that provides the traditional power and lifetime capabilities of a metal-air cell in a low cost, efficient manner.
The present invention seeks to provide a removable metal-air cell pack used to power an electrical device, to protect the cell pack from negative effects of ambient air when power is not demanded from the cell pack, and to avoid the need to supply an air moving device with every cell pack.
The present invention accomplishes this object by providing in combination (1) a cell pack that includes one or more isolation passageways positioned to protect the metal-air cell or cells from the ambient air when no air mover is active to force air to the cell or cells, and the passageway or passageways remain unsealed, and (2) an electrical device configured to removably receive the cell pack in a manner which allows an air mover associated with the electrical device to communicate with at least one of the isolation passageways of the cell pack to provide air to the cell or cells.
In one embodiment of the present invention the isolation passageway is an isolating or a diffusion pathway in the form of a tube or tubes. An intake pathway and an exhaust pathway may be used or, alternatively, a single pathway may be used.
Generally described, the present invention provides a battery powered device, comprising a removable metal-air battery including a ventilation passageway communicating between an interior and an exterior of said battery; a docking station at which said metal-air battery may be removably mated; an air moving device exterior to said metal-air battery; and an upstream passageway communicating between said air moving device and said ventilation passageway of said metal-air battery when said metal-air battery is mated at said docking station, said ventilation passageway being sized to restrict air flow therethrough while said ventilation passageway remains unsealed and the air moving device is inoperative.
In a preferred embodiment, said ventilation passageway comprises a diffusion tube, and may be paired with an outlet diffusion tube depending on the nature of the air mover, which may be a fan, or a reciprocating air mover such as a diaphragm pump. The device may further comprise a perforated plate defining apertures positioned to receive and uniformly distribute air flow from said inlet diffusion tube to one or more air electrodes within said metal-air battery.
The diffusion tubes preferably have a length to width ratio of at least 10 to 1. In a preferred embodiment, they have a length of about 0.3 to 2.5 inches, and a width of about 0.03 to 0.3 inch.
According to another of its aspects, the invention provides, in combination, an air manager and a metal-air battery, said metal-air battery comprising one or more metal-air cells and a ventilation passageway communicating between an interior and an exterior of said battery; and said air manager comprising a housing comprising a docking station at which said metal-air battery may be removably mated with said housing; a air moving device positioned within said housing; and an upstream passageway connecting said air moving device to an opening positioned so as to communicate with said ventilation passageway of said metal-air battery when said metal-air battery is mated at said battery port; said ventilation passageway being sized to restrict air flow therethrough while said passageway remains unsealed and the air moving device is inoperative.
According to another of its aspects, the invention provides electronic device powered by a metal-air battery including an input diffusion tube, comprising a battery port at which said metal-air battery may be removably mated with said electronic device; an air moving device positioned within said electronic device; and a passageway connecting said air moving device to an outlet positioned so as to communicate with said input diffusion tube of said metal-air battery when said metal-air battery is mated at said battery port, being sized to restrict air flow therethrough while said passageway remains unsealed and the air moving device is inoperative.
A further embodiment includes an electronic device driven by a metal-air battery with an input diffusion tube. The electronic device has an exterior surface and a battery port for mating with the metal-air battery. The device also has an intake diffusion tube positioned within the device so as to communicate between the exterior and the input diffusion tube of the metal-air battery when the metal-air battery is positioned within or adjacent to the battery port. A fan is positioned within the intake diffusion tube of the electronic device. This embodiment results in a replaceable metal-air battery for mating with an electrical device with an internal fan for providing reactant air.
The present invention provides a metal-air power supply having at least one metal-air cell. The power supply also has at least one passageway capable of passing sufficient air to operate the cell when operatively associated with an operating air moving device. The passageway is further operative, while unsealed and not under the influence of the operating air movement device, to restrict airflow through the passageway. The air movement device itself is separable from the power supply.
A further embodiment of the present invention provides a two-part metal-air cell. The cell has an air manager cap with an air manager pathway positioned within the cap. The air manager pathway has an air inlet and a cap mating connector. An air movement device is positioned to cause a flow of air within the air manager pathway. The cell housing also has a chemistry body that is detachable from the air manager cap. The chemistry body has a chemistry body diffusion pathway with a body mating connector. The cap mating connector and the body mating connector are sized to mate with each other when the cap and chemistry body are brought into engagement. The air movement device may be capable of reciprocating motion.
The invention, also provides a metal-air battery having a distributor for approximately uniformly distributing oxygen-laden air to multiple oxygen electrodes, which may be associated with one or more metal-air cells, in response to operation of an air moving device. As a result of the distribution of oxygen, each of the metal-air cells operate at approximately the same current (when the cells are arranged in parallel) and voltage (when the cells are arranged in series) so that the battery provides an optimum amount of electrical power over an extended period of time.
Preferably the distributor is further operative, or associated with one or more restrictive passageways that are operative, while unsealed to provide a barrier function that protects the metal-air cells from the ambient environment at the appropriate time, such as while the air moving device is not operating. That is, while the air moving device is off, or not providing air to the metal-air battery, the distributor and/or restrictive passageway or passageways restrict air flow to the oxygen electrodes so that the metal-air battery is capable of having a long shelf life without requiring), a door or doors, or the like, to seal the oxygen electrodes from the ambient environment.
In accordance with one aspect of the invention, a ventilation system is provided for supplying air to a metal-air cell assembly having at least a first oxygen electrode and a second oxygen electrode. The ventilation system has a housing that defines a chamber for receiving the metal-air cell assembly. The ventilation system further includes an air moving device for moving air through a reactant air flow path to the chamber. The ventilation system further includes a perforated member that is positioned in the reactant air flow path for distributing air flow approximately uniformly through the chamber in response to operation of the air moving device. The perforated member may also restrict air flow to the chamber while the air moving device is not providing air to the metal-air battery and the reactant air flow path is unsealed, or alternatively another component defines a restriction in the reactant air flow path that restricts air flow to the chamber while the air moving device is not providing air to the metal-air battery and the reactant air flow path is unsealed.
In another aspect of the present invention, a metal-air power supply is provided. The metal-air power supply includes a first plenum communicating with a first oxygen electrode and a second plenum communicating with a second oxygen electrode. The metal-air power supply further includes a perforated member that is positioned within the reactant air flow path for distributing air flow approximately uniformly between the plenums in response to operation of an air moving device. The perforated member may also restrict air flow to the plenums while the air moving device is off and the reactant air flow path is unsealed, or alternatively another component defines a restriction in the reactant air flow path and restricts air flow to the plenums while the air moving device is not providing air to the metal-air power supply and the reactant air flow path is unsealed.
In another aspect of the invention, the metal-air power supply may be docked to an electronic device that is powered by the metal-air power supply. The electronic device may at least partially define the reactant air flow path, and may include the air moving device and the restriction in the reactant air flow path that restricts air flow to the plenums while the air moving device is off and the air flow path is unsealed.
The air moving device may sweep a continuous flow of fresh air from the ambient environment across the oxygen electrodes at a flow rate sufficient to achieve the desired power output. Alternatively, the air moving device may recirculate air across the oxygen electrodes, and the air moving device may further move air through one or more passageways to refresh the recirculating air.
Regarding the perforated members in greater detail, each preferably defines a plurality of apertures that at least partially define the reactant air flow path, and each aperture defines a width perpendicular to the direction of flow therethrough and a length in the direction of flow therethrough, the length being, one or multiple times greater than the width. The perforated member may be a plate, or it may be an elongate ventilation passageway, such as a tube, having the apertures distributed along its length. A first of the apertures is more proximate to a first plenum than a second plenum and a second of the apertures is more proximate to the second plenum than the first plenum. Alternatively the perforated member may be in the form of a bundle of tubes; an aggregate of materials that define air paths therebetween, such as a bundle of fibers with air paths defined between the fibers; a piece or porous material that is preferably thick; or the like.
In another aspect of the invention, the aforementioned oxygen electrodes are part of a stack of metal-air cells. The metal-air cells may have spaced protrusions, and the air moving device may be mounted between protrusions of the cells. Further, each metal air cell includes a case. Each case may include a pair of unitary case portions, each of which has side walls extending from a panel in a common direction to define a cavity. For each cell, a first case portion is mounted to a second case portion such that the side walls of the first case portion extend into the cavity of the second case portion.